1. Field of the Disclosure
The embodiments described herein relate generally to pulse fracturing devices and methods, for example, to a dual valve device configured to produce cyclic pulses of increased pressure in a well bore.
2. Description of the Related Art
Fracture stimulation, a known practice in the oil and gas industry, may be used to increase the production of hydrocarbons from wells, such as in lower quality reserves. Known practices include forming a well bore in a subterranean formation and inserting a well casing in the well bore. Horizontal well bores may be formed to increase the extent to which a single well bore may reach desired regions of a formation. Horizontal wells as a percentage of newly drilled wells continue to rise. Multiple fracture stages may be implemented in a single well bore to increase production levels and provide effective drainage. Perforations in sections of a well casing allow fracturing fluid at high pressure to initiate and then propagate a fracture in the formation during each stage. A proppant included in the fracturing fluid may lodge in the fracture to keep it propped open after fracturing, increasing conductivity. For effective fracturing, one section may be fractured at a time by hydraulically isolating other perforated sections. A variety of mechanisms, e.g. bridge plugs, and materials, e.g. sand plugs, are known to allow hydraulic isolation.
Techniques have been developed whereby perforating and fracturing operations are performed with a coiled tubing string. One such technique is known as the Annular Coil Tubing Fracturing Process, or the ACT-Frac Process for short, disclosed in U.S. Pat. Nos. 6,474,419, 6,394,184, 6,957,701, and 6,520,255. To practice the techniques described in the aforementioned patents, the work string, which includes a bottom hole assembly (BHA), generally remains in the well bore during the fracturing operation. One method of perforating, known as the sand jet perforating procedure, involves using a sand slurry to blast holes through the casing, through the cement, and into the well formation. Then fracturing can occur through the holes.
Well completion techniques that do not involve perforating are known in the art. One such technique is known as packers-plus-style completion. Instead of cementing the completion in, this technique involves running open-hole packers into the well hole to set the casing assembly. The casing assembly includes ported collars. After the casing is set in the well, the ports can be opened. Fracturing can then be performed through the ports.
A variety of mechanisms and systems have been devised to allow fracturing in selected sections of a well bore by opening selected ports. Examples are described in U.S. patent application Ser. No. 12/842,099 entitled “BOTTOM HOLE ASSEMBLY WITH PORTED COMPLETION AND METHODS OF FRACTURING THEREWITH,” filed Jul. 23, 2010, by Lyle E. Laun and John Edward Ravensbergen, which is incorporated by reference herein in its entirety. Another technique for fracturing wells without perforating is described in U.S. patent application Ser. No. 12/826,372 entitled “JOINT OR COUPLING DEVICE INCORPORATING A MECHANICALLY-INDUCED WEAK POINT AND METHOD OF USE,” filed Jun. 29, 2010, by Lyle E. Laun.
Whether fracturing fluid flows through casing perforations or ports, it is known to fracture using pulses of increased pressure instead of just sustained or ramping pressure. U.S. Pat. No. 2,915,122 issued to Hulse describes applying cyclic pressure shocks to form a greater plurality of relatively small fractures using an air hammer or piston at the well head. U.S. Patent Application Publication No. 2011/0108276 by Spence et al. (hereinafter “Spence et al.”) describes applying repeated pressure pulses to enhance formation dilations. Spence et al. uses a plug that temporarily seals against a die in a wellbore and increases pressure until the plug passes through the die, releasing the increased pressure to the target formation. U.S. Pat. No. 5,005,649 issued to Smith et al. describes applying a pressure pulse to form multiple fractures in a fracture zone using rupture discs on high-pressure tubing. Accordingly, further advancement in pulse fracturing devices and methods may be of benefit.